1. Field of the Invention
The present invention relates to a rotary sensor capable of detecting a rotational angle transmitted from the outside for use as a throttle sensor of an automobile.
2. Description of the Related Art
A conventional rotary sensor will be described with reference to FIG. 12. A casing 51 is composed of a case 52 molded of a synthetic resin and a lid 53 covering an opening formed in the rear of the case 52.
The case 52 includes a sidewall 52b having an accommodation portion 52a formed within the sidewall 52b, a cylindrical receiving portion 52c protruding from the sidewall 52b into the accommodation portion 52a, a double-step shoulder 52d formed in the rear of the sidewall 52b adjacent to an opening, and a cylindrical section 52e formed so as to extend from the sidewall 52b. 
The disk-shaped lid 53, including a cylinder section 53a disposed at the center, is placed on a shoulder 52d from the opening in the rear of the case 52, and is attached to the case 52 so as to close the opening by thermally caulking the rear of the sidewall 52b of the case 52.
A plurality of metallic terminals 54 for use as connectors are embedded in and attached to the case 52 with one end protruding within the accommodation portion 52a of the case 52 and with the other end protruding within the cylindrical section 52e. 
A metallic support section 55 is formed in a truncated conical shape, and is held by inserting it into the cylinder section 53a. 
A plate-like insulating substrate 56 has a hole 56a in the center, and is provided with an annular resistor pattern and a collector pattern (not shown) composed of a good conductor, which are formed on one surface of the insulating substrate 56. The resistor pattern and the collector pattern are in a state conducting electricity to a plurality of terminals 57 attached to the insulating substrate 56.
The periphery of the insulating substrate 56 is placed on the shoulder 52d so as to accommodate the insulating substrate 56 within the accommodation portion 52a in a state that the hole 56a is opposing the support section 55. The insulating substrate 56 is attached to the case 52 by pushing the external periphery of the insulating substrate 56 to the shoulder 52d by the lid 53 attached to the case 52, while the terminal 57 is connected with solder to the terminal 54, which is used for a connector and protrudes in the accommodation portion 52a. 
A rotator 58 molded with a synthetic resin includes a disk section 58a, a cylindrical section 58b disposed in front of the center of the disk section 58a, a concave accommodating section 58c disposed within the cylindrical section 58b, a cylinder section 58d disposed on the bottom surface of the disk section 58a, and a concave engaging section 58e formed in the accommodating section 58c. 
The rotator 58 is accommodated within the accommodation portion 52a of the case 52, and is rotatably held by inserting the cylindrical section 58b into the receiving portion 52c also by inserting the cylinder section 58d into the hole 56a of the insulating substrate 56 so that the support section 55 is fitted into the cylinder section 58d. Also, the rotator 58 is pivotablly supported by the support section 55 so as to enable the rotator 58 to incline.
An elastic member 59 is made of a ring-shaped rubber material, and arranged between the disk section 58a of the rotator 58 and the upper wall of the accommodation portion 52a. Also, the rotator 58 is constantly pushed to the support section 55 by a waving washer 63.
A sliding contact 60 is made of a conductive springing plate in a substantial arc shape. The sliding contact 60 is placed on the bottom surface of the disk section 58a, and its arc-shape portion is arranged along the circumferential direction of the disk section 58a by appropriate means while the end of the sliding contact 60 is attached to the rotator 58. The sliding contact 60 is slidable over a resistor pattern and a collector pattern in a deflected state. The resistor pattern, the collector pattern, and the sliding contact 60 constitute a detecting unit K2 composed of a rotary variable resistor for detecting a rotation angle.
An elastic member 61 made of a material with a springing property is formed in a U-shape as a whole by folding it into two, and includes an anchoring section 61a formed by cutting-up. The elastic member 61 is accommodated within the accommodating section 58c of the rotator 58, and the anchoring section 61a is brought into engagement with the engaging section 58e. 
A drive shaft 62 connected to a throttle valve of an automobile or the like includes a projection 62a disposed at its end and extending in the direction of the axial line A. The drive shaft 62 reciprocally rotates in a predetermined rotational angle range.
The drive shaft 62 is inserted into the accommodating section 58c of the rotator 58, and pressed into contact with the internal wall of the accommodating section 58c by the elastic member 61, while the elastic member 61 is also pressed into contact with the internal wall of the accommodating section 58c. 
In the rotary sensor having such a structure, during the rotation of the drive shaft 62, the rotator 58 is rotated because the projection 62a is pressed into contact with the rotator 58 by the elastic member 61. As a result, the sliding contact 60 slides over the resistor pattern and the collector pattern so as to operate the detecting unit K2 for detecting the rotational angle (see Japanese Unexamined Patent Application Publication No. 2002-39789, for example).
In general, in a conventional rotary sensor, if the pushing force from the drive shaft 62 to the rotator 58 is reduced, when the drive shaft 62 rapidly rotates, the elastic member 61 is twisted so as to produce the delaying the rotational transmission by the rotator 58, deteriorating the followingness of the rotator 58 relative to the drive shaft 62. For this reason, a strong pushing force from the drive shaft 62 to the rotator 58 is generally employed.
If the pushing force from the drive shaft 62 to the rotator 58 is increased, even when the drive shaft 62 rapidly rotates, the followingness of the rotator 58 relative to the drive shaft 62 is improved.
The drive shaft 62 has backlash in the direction of the axial line A because of errors in mounting, so that the drive shaft 62 may be moved in the direction of the axial line A (Z1 and Z2 directions) by vibration, etc.
In the state that the pushing force from the drive shaft 62 to the rotator 58 is strong, when the drive shaft 62 moves in the Z2 direction (direction of the drive shaft 62 coming off the rotator 58), if the combined frictional force of the frictional force between the drive shaft 62 and the elastic member 61 and that between the drive shaft 62 and the rotator 58 is increased larger than the combined force of the pushing force from the waving washer 63 to the rotator 58 and the frictional force in the Z1 direction between the elastic member 59 and the rotator 58, the rotator 58 moves so as to follow the movement of the drive shaft 62 in the Z2 direction.
Then, the height of the sliding contact 60 in use changes, so that the contact position to the resistor pattern in the circumferential direction is changed so as to change the value of resistance. As a result, the detection of the rotational angle fluctuates so as to deteriorate performances, so that during the movement of the drive shaft 62, the rotator 58 is prevented from moving by increasing the pushing force of the waving washer 63 larger than the combined frictional force of the frictional force between the drive shaft 62 and the elastic member 61 and that between the drive shaft 62 and the rotator 58.
If the pushing force of the waving washer 63 is increased in such a manner, the rotational moment required for rotating the rotator 58 must be increased. As a result, the twist amount of the elastic member 61 is increased so as to produce the delaying the rotational transmission by the rotator 58, deteriorating the followingness of the rotator 58 relative to the drive shaft 62.
In addition, as for the movement of the drive shaft 62 in the Z1 direction, the contact position of the sliding contact 60 to the resistor pattern is scarcely changed because one end of the rotator 58 is supported by the support section 55.
The elastic member 61 is retained to the rotator 58 with the anchoring section 61a while since the projection 62a of the drive shaft 62 is formed by cutting so as to have a rough surface, the projection 62a may have a large frictional coefficient by erosion during the usage.
Then, the combined frictional force of the frictional force between the drive shaft 62 and the elastic member 61 and that between the drive shaft 62 and the rotator 58 is increased larger than the pushing force from the waving washer 63 to the rotator 58, so that the rotator 58 eventually moves so as to follow the movement of the drive shaft 62 in the direction of the axial line A (Z1 and Z2 directions).
Then, when the rotator 58 moves in the Z2 direction, as described above, the gap between the rotator 58 and the insulating substrate 56 is changed so that the contact position of the sliding contact 60 to the resistor pattern changes so as to change the value of resistance. As a result, the detection of the rotational angle fluctuates so as to deteriorate performances.
Furthermore, in the state that the pushing force by the drive shaft 62 to the rotator 58 is increased or that the frictional coefficient is increased by the erosion of the projection 62a, if the casing 51 expands by the external heat, since an annular flange formed on a sidewall of the case 52 is firmly held to an engine with screws, the insulating substrate 56 and the lid 53 supported by the case 52 are pushed downward, i.e., in the Z1 direction (the direction of the support section 55 separating from the rotator 58). At this time, since in comparison with the pushing force from the waving washer 63 in the Z1 direction, the contacting force is larger or the combined force of the frictional force between the rotator 58, the elastic member 61, and the rotator 58 and the sliding pressure of the sliding contact 60 is larger, the rotator 58, the elastic member 61, and the drive shaft 62 are not moved while the insulating substrate 56 and the lid 53 move in the state that the initial positions are maintained.
Then, the gap between the rotator 58 and the insulating substrate 56 is changed so that the contact position of the sliding contact 60 to the resistor pattern changes so as to change the value of resistance. As a result, the detection of the rotational angle fluctuates so as to deteriorate performances.
When the case 52 contracts after expansion, the insulating substrate 56 returns to the original position, and the gap is changed so that the contact position of the sliding contact 60 to the resistor pattern changes so as to change the value of resistance. As a result, the detection of the rotational angle fluctuates so as to deteriorate performances.
In a conventional rotary sensor, since the pushing force of the waving washer 63 is increased larger than the combined frictional force of the frictional force between the drive shaft 62 and the elastic member 61 and that between the drive shaft 62 and the rotator 58 so as to not move the rotator 58 during the movement of the drive shaft 62, the rotational moment required for rotating the rotator 58 must be increased. As a result, there is a problem that the amount of twist of the elastic member 61 is increased, so that the rotational transmission by the rotator 58 is delayed, deteriorating the followingness of the rotator 58 relative to the drive shaft 62.
If the drive shaft 62 is eroded in use, the coefficient of friction is increased, so that the combined frictional force of the frictional force between the drive shaft 62 and the elastic member 61 and that between the drive shaft 62 and the rotator 58 is increased larger than the value subtracting the sliding pressure of the sliding contact 60 from the pushing force by the waving washer 63 to the rotator 58. As a result, the rotator 58 moves to follow the movement of the drive shaft 62 in the direction of the axial line A (Z2 direction), and the gap between the rotator 58 and the insulating substrate 56 is changed so that the contact position of the sliding contact 60 to the resistor pattern changes so as to change the value of resistance. Therefore, the detection of the rotational angle fluctuates so as to deteriorate performances.
During the expansion and cotraction of the case 52 of the casing 51, the gap between the rotator 58 and the insulating substrate 56 is changed so that the contact position of the sliding contact 60 to the resistor pattern changes so as to change the value of resistance. As a result, there is a problem that the detection of the rotational angle fluctuates so as to deteriorate performances.